On rhododendron hybridization

Last summer (2015) I did only a few crosses. After a long while Henry's Red and Böhmen bloomed, so I could use them as mothers. The following crosses produced a fair amount of seeds that I sew today (a bit late this year):

I finally managed to clean all the seeds from this year's crosses. I collected the seedpods in plastic cups in early October (some had started to open, so I was a bit too late) and let them dry at room temperature for several weeks. Pods of some cultivars open nicely and almost all seeds fall of, others don't. For example, the pods of Queen Anne's have to be split open manually or crushed to release the seeds properly. Here is a list of the crosses that produced any seeds this year. Lem's Monarch that I wrote about earlier was a disappointment as seed parent, none of the pollinations took. On the contrary, LM worked well as a pollen parent. Other disappointments were the poor fertility of Weissenburg, the double flowered hybrid I bought this year. Only one cross to Weissenburg produced any seeds. The poor success of pollinations with Honigduft pollen was another unpleasant suprise.

1. Helsinki University X R. thomsonii (*)

2. Helsinki University X Lem's Monarch (*)

3. Bellefontaine X Lem's Monarch

4. Bellefontaine X Dufthecke

5. Catawbiense Borsault X Honigduft

6. Haaga X Lem's Monarch

7. Mikkeli X Honigduft

8. Mikkeli X Lem's Monarch

9. (SFxPMAT1) X Haagan keltainen

10. (SFxPMAT1) X (bvt X Lemonade)

11. Queen Anne's X Catawbiense Borsault (*)

12. Queen Anne's X Lem's Monarch (*)

13. Weissenburg X Kuutamo

Azalea crosses etc.

14. MM1 X Mustila oranssi (*)

15. R. arborescens X MM1 (*)

16. Lemondrop X R. arborescens (*)

17. Haaga X MM1

From the crosses marked with (*) I have enough seeds to be given away. E-mail jpkrvi (at) yahoo.co.uk if you are interested in obtaining any of these seeds.

MM1 = yellow-flowered luteum-like azalea grown by me from Mustila arboretum seed mix, pollen extremely fertile

Mustila oranssi = pollen from an unnamed bright orange-flowered azalea from Mustila arboretum 

I had a few small trays of seedlings from my azalea crosses of 2011 that I decided need to be transplanted out before they become two crowded. Very beautiful, lush seedlings. For example, R. prinophyllum X R. occidentale (see photo). Since there was only 5-10 plants from each cross and I don't have a proper trial field for the seedlings I made individual, round beds for each batch in a half-shady "meadow" on the property. The meadow has rather thing, hard mixed moraine-clay soil, so (after killing weeds with glyphosate) I mix a wheelbarrow full of well-rotted horse manure and a bag of cheap, commercial compost, make a round bed with a depth of 15-20 cm and plant the seedlings in that. Finally, I cover the surface with a thin layer of home-made mulch (wood chips) and water well. These mini beds turned out to retain moisture very well even during our exceptionally hot July month and the azalea seedlings look great now in mid-August. I have transplanted about 7 batches of rhododenron seedlings similarly. I hope these conditions will allow at least most of the plants to reach flowering size before they get too crowded.

Three surviving seedlings from my cross Dorte Reich X Ledum palustre. It is known from the work of other hybridizers that Ledum palustre can be crossed with several other lepidotes when used as pod parent. I wanted to test if it works as pollen parent and apparently it does, at least on Dorte Reich. By now I'm absolutely sure that these seedlings are hybrids as they resemble Ledum seedlings in leaf morphology and have the unmistakable, pungent ledum scent. DR also has aromatic foliage but the scent is very different, much sweeter. Interestingly, recent ploidy analysis shows that DR is polyploid. As all tested Finnish ledum samples have proven tetraploid (and I collected the pollen from plants in a local bog) there are fair chances that this cross will produce fertile offspring, which might open an interesting new breeding path towards hardy lepidotes.

This is actually not completely true as a few of my own R. canadense seedlings bloomed last summer but other than that these are the first. The azalea I grew from a seed mix bought in the Mustila arboretum. Nothing special really, but a nice plant similar to the R. luteum species. The flowers are rather small and have a very strong yellow azalea scent. The flowers produce ample amounts of pollen, which is good since I have very little azalea pollen in store right now. I pollinated this one (named MM1) with a few different pollens to find out if it is fertile.

The other delightful first flowering (below) is from one of my first hand pollinations ever: September Flair X P.M.A. Tigerstedt (2008). Small flowers (like in both parents) but very nice picotee colouring. The flowers are almost exactly halfway between the parents. The flowers turned out to be very long lasting (about 2 weeks) even though I hand pollinated them. This plant (SFxPMAT1) does not seem to produce any pollen, which is similar to its female parent.